In recent years, vehicle theft and theft of various equipment provided at an interior of a vehicle, and the like have frequently occurred. In the thefts, a case where a key cylinder of a vehicle door is broken to unlock a door lock of the vehicle door from the outside of the vehicle and a case where a window glass of the vehicle is broken to operate an inner lock of the vehicle door to thereby unlock the door lock from the inside of the vehicle are considered. When the vehicle door is unlocked in the aforementioned manners, an intrusion to the inside of the vehicle is easily executed.
In order to prevent unlocking of the vehicle door from the outside of the vehicle, the key cylinder is eliminated and, instead, a key-less entry system, an intelligent key, a smart key or the like is used to avoid the breakage of the key cylinder. Alternatively, a door lock system is changed to an electronic system. In addition, in order to prevent unlocking of the vehicle door from the inside of the vehicle, an alarm system that is activated when a sound of a broken window glass is detected, an apparatus for obscuring the inside of the vehicle by a change of color of the window glass, and the like have been proposed.
JP2572576Y (hereinafter referred to as Reference 1) discloses an antitheft device for a vehicle that sounds an alarm, and the like when detecting the sound of a broken window glass. The antitheft device disclosed in Reference 1 includes a function for preventing a wrong detection. JP2007-276561A and JP2003-136957A (hereinafter referred to as Reference 2 and Reference 3, respectively) each disclose an antitheft device for a vehicle that decreases visibility of an inside of the vehicle when it is seen through a window glass in a case where no passengers are present inside of the vehicle. JPH11-198648A (hereinafter referred to as Reference 4) discloses a pinch detection device for detecting an intrusion from between a window glass and a window frame by using an optical sensor provided at a center pillar. JP2003-141649A and JP2006-252499A (hereinafter referred to as Reference 5 and Reference 6, respectively) disclose a glass breakage detection device and a security system for detecting a glass breakage. JP2003-170739A (hereinafter referred to as Reference 7) discloses a window glass for a vehicle constituted by a heat reflecting glass, a power heated glass, or the like of which transmittance of a radio wave is enhanced.
According to the antitheft device disclosed in Reference 1, an addition of a microphone sensor is required to detect the sound of a broken window glass. In this case, the microphone sensor may mistakenly detect an external sound as that of the sound of a breaking glass. The antitheft devices disclosed in References 2 and 3 are technologies related to visibility effectiveness and thus are not able to detect an intrusion of an individual into the vehicle when the window glass is broken. According to the pinch detection having an intrusion detecting unction disclosed in Reference 4, the optical sensor is provided at an upper portion in the vicinity of the window frame, which may be obtrusive for a passenger and a hindrance to an ingress and egress of the passenger. The glass breakage detection device disclosed in Reference 5 and the security system disclosed in Reference 6 each utilize a voltage when a window glass is broken and a voltage when the window glass is not broken. That is, the voltages before and after the window glass is broken are compared to detect if the window glass is broken. When the window glass is partially broken, i.e., not fully broken, the voltage specified to be a detection signal may be still applied to the detection portion because of a non-disconnection state of a resistor or a conductive wire provided at the window glass. Thus, even when the glass is broken, no difference is found between the voltages before and after the breakage of the glass, which may lead to a non-detection (i.e., wrong detection) of the breaking glass.
A need thus exists for an abnormality detecting apparatus which is not susceptible to the drawback mentioned above.